Final answer:
Arrows crossing the center line in a workflow diagram often signify relationships between objects or phases within a system or process, such as economic flows or sequential project steps.
Step-by-step explanation:
In a workflow diagram, the arrows that cross the center line are typically used to illustrate the flow of a process, and can represent various relationships and activities depending on the context of the diagram. After evaluating the given options, it is likely that the arrows which cross the center line identify relationships between objects or entities within the system or process being depicted. These arrows can illustrate pathways of influence, sequences of events, or movements between different phases, rather than literal flows of matter or energy. For example, in an economic model, arrows can represent imports and exports or payments for these, all being crucial interactions in a system or process. Similarly, in a phased project approach, arrows might indicate the transition from one phase to the next, such as from a Preparatory Phase to an Implementation and Learning Phase.